Medical lead with preformed bias

ABSTRACT

A medical electrical lead and methods of implanting medical electrical leads in lumens. Leads in accordance with the invention employ preformed biases to stabilize the lead within a lumen and to orient electrodes in a preferred orientation.

BACKGROUND

Electrical stimulation or sensing leads for providing medical therapyare being used in an increasing number of applications. Leads have beenimplanted in patients' hearts, along the spinal column, and in otherloctions to deliver appropriate therapy or sense physiologic conditions.Increasingly leads are implanted in veins, arteries, or other lumens tostimulate or sense tissue near the lumens.

The implantation of electrical leads in lumens presents opportunitesbecause the leads can be fed into the patient's body and implantedwithout the surgery necessary to install nerve cuffs and othersurgically implanted electrodes. Implanting leads in lumens also reducesthe possibility of post-surgical trauma or damage to the tissue beingstimulated or sensed. Difficulties associated with implanting leads inlumens include issues with lead migration and difficulty orienting thelead and electrodes.

Typical electrical leads have a proximal end that is connected to anelectrical pulse generator or to circuitry configured to process signalssensed by electrodes on the leads. The electrodes.on the leads areconnected to the distal end by flexible and durable conductors, whichare ultimately connected to an external or implantable medical devicecontaining the requied circuitry to detect sensed signals ot to deliverstimulation therapy.

SUMMARY

In one embodiment in accordance with the invention, a medical electricallead includes a lead body having a preformed helical bias with a coildiameter. The lead also has at least one electrode, and the ratio of thecoil diameter to the length of the at least one electrode is at least4:1. In other embodiments, this ratio is at least 5:1 or 6:1.

In another embodiment in accordance with the invention, a medicalelectrical lead includes a lead body having a preformed helical biaswith a coil diameter. The preformed helical bias of this embodiment is aconverging helical bias and the coil diameter is defined as the diameterof the smallest coil of the bias. The lead also has at least oneelectrode, and the ratio of the coil diameter to the length of the atleast one electrode is at least 4:1. In other embodiments, this ratio isat least 5:1 or 6:1.

In another embodiment in accordance with the invention, a medicalelectrical lead includes a lead body having a preformed helical biaswith a coil diameter. The preformed helical bias of this embodiment is adiverging helical bias and the coil diameter is defined as the diameterof the smallest coil of the bias. The lead also has at least oneelectrode, and the ratio of the coil diameter to the length of the atleast one electrode is at least 4:1. In other embodiments, this ratio isat least 5:1 or 6:1.

In another embodiment in accordance with the invention, a medicalelectrical lead includes a lead body having preformed helical bias witha coil diameter. The lead of this embodiment includes a plurality ofelectrodes, and at least a portion of each of the plurality ofelectrodes is within a single quadrant of the helical bias. In anotherembodiment, each of the electrodes has a length such that ratio of thecoil diameter to the lengths of the electrodes is at least 4:1. In otherembodiments, this ratio is at least 5:1 or 6:1.

In yet another embodiment in accordance with the invention, a medicalelectrical lead includes a lead body having a lead body axis. There is apreformed bias in the lead body, and the bias has a bias axis. The anglebetween the lead body axis and the bias axis of this embodiment isgreater than thirty degrees. In other embodiments, the angle between thelead body axis and the bias axis is greater than forty-five degrees.

Another embodiment in accordance with the in vention is a method ofimplanting a lead in a lumen including the steps of inserting a lead ina lumen, the lead having a helical bias and a plurality of electrodeswherein at least a portion of each of the plurality of electrodes iswithin a single quadrant of the helical bias. The method also has a stepof positioning the lead within the lumen so that a tissue of interest iswithin the quadrant as the quadrant extends outward radially.

In another embodiment, a method of implanting a lead in a lumen includesthe steps of inserting a lead in a lumen, the lead having a helical biasand a plurality of electrodes wherein at least a portion of each of theplurality of electrodes is within a single quadrant of the helical bias.The method also includes a step of positioning the lead within the lumenso that a tissue of interest is within the quadrant as the quadrantextends outward radially.wherein the lumen includes the rightbrachiocephalic vein and the tissue of interest comprises the rightphrenic nerve. In other embodiments the lumen includes the leftbrachiocephalic vein and the tissue of interest includes the leftphrenic nerve, the lumen includes the superior vena cava and the tissueof interest includes the right phrenic nerve, the lumen includes theright internal jugular vein and the tissue of interest includes thehypoglossal nerve, or the lumen comprises the junction between the rightbrachiocephalic vein and the right subclavian vein.

BRIEF DECRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lead in accordance with embodiments ofthe invention.

FIG. 2 is a perspective view of a lead in accordance with embodiments ofthe invention.

FIG. 3 is a perspective view of a lead in accordance with embodiments ofthe invention.

FIG. 4 is a perspective view of a lead in accordance with embodiments ofthe invention.

FIG. 5 is a plan view of a lead in accordance with embodiments of theinvention.

FIG. 6 is a schematic view of a lead in accordance with embodiments ofthe invention implanted in a patient.

FIG. 7 is a schematic view of a lead in accordance with embodiments ofthe invention implanted in a patient.

FIG. 8 is a schematic drawing of a lead in accordance with embodimentsof the invention implanted in a cross section of a lumen.

FIG. 9 is a schematic drawing of a lead in accordance with embodimentsof the invention as in FIG. 8 from a view along an axis such as B.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a lead in accordance with embodiments ofthe invention. The lead has a lead body 10 with a proximal portion 20and a distal end 30. Electrodes 40 are distributed along a distalportion of the lead body 10. A bias region 50 near the distal end isformed in a helical or circular fashion. This bias region 50 may beformed by wrapping the lead around a spindle of other shape impartingstructure and heat treating or otherwise shaping the lead body 10 in away that the lead will be biased to return to this preformed shape. Thelead body may be constructed from a shape memory polymer or metal or ofany material suitable for the purpose. If constructed from a shapememory polymer, for example polyurethane, the thickness or diameter ofthe lead body or other parameters may be varied to adjust the degree ofrigidity of the bias.

The bias may be helical or generally circular. The primary differencebetween what is described herein as a helical bias and a circular biasis the pitch of the helix. A circular bias is one in which the pitch ofthe helix is less than or equal to the thickness of the lead. That isthe coils of the helix touch or overlap with one another when the leadis in its unstressed position. If the pitch of the helix is greater thanthe thickness of the lead, the bias is referred to herein as helical.For the purposes of this discussion, circular and helical biases areinterchangeable unless specifically noted as the pitch is essentiallythe only difference.

The bias 50 shown in FIG. 1 is generally is a helix of a constantdiameter. This embodiment is usable to secure a lead within a relativelylarge lumen. In practice, the diameter of the helix is designed to beslightly larger than the lumen in which it is implanted, and thepressure of the bias against the lumen wall retains the lead within thelumen. Once so retained, the electrodes are in a position to senseactivity in nearby tissues or electrically stimulate nearby tissues.

As an example, the embodiment of FIG. 1 could be implanted within theright or left brachiocephalic vein or superior vena cava of a patient.Both the right and left brachiocephalic veins are similar in size,ranging from approximately 15 mm to 22 mm in diameter. An embodiment forthis application may, for example, have a helix/coil diameter of 20 mm.The helix/coil length, measured along the axis of the helix from thefirst curvature to the end of the lead, may in this example be 30-40 mm.

FIG. 2 is a perspective view of a lead in accordance with embodiments ofthe invention. Like the embodiment in FIG. 1, this embodiment has a leadbody 10 with a proximal portion 20 and a distal end 30. Electrodes 40are disposed generally distally on the lead body. A bias 50 is formed ina helical or circular fashion near the distal end. This bias 50 isformed as a converging circle or helix, with the coils having adecreasing diameter from the proximal portion 20 toward the distal end30.

A lead in accordance with FIG. 2 could be usable to secure electrodeswithin lumens at a junction of two or more lumens. If a lumen or vesseldiverges to form two, for example, this lead could be employed such thatthe larger diameter coils of the helix are deployed within the largerdiameter region where the lumens diverge while the smaller diametercoils reside within the single lumen formed by the junction. In thismanner, a consistent anchoring pressure may be provided in a region ofdiverging diameters due to a junction of lumens.

FIG. 3 is a perspective view of a lead in accordance with embodiments ofthe invention. The embodiment of FIG. 3 includes a lead body 10 having aproximal portion 20 and a distal end 30. One or more electrodes 40 aredisposed along the lead body. A bias 50 is formed proximate the distalend 30. The bias in this embodiment has a diverging circle or helix, inwhich the diameter of the coils increases from the proximal portion 20to the distal end 30. If a two lumens or vessels converge to form one,for example, this lead could be employed such that the larger diametercoils of the helix are deployed within the larger diameter region wherethe lumens come together while the smaller diameter coils reside withinthe single lumen formed by the junction. In this manner, a consistentanchoring pressure may be provided in a region of converging diametersdue to a junction of lumens.

FIG. 4 is a perspective view of a lead in accordance with embodiments ofthe invention. The embodiment of FIG. 4 includes a lead body 10 having aproximal portion 20 and a distal end 30. A circular or helical bias 50is proximate the distal end. Electrodes 40 are disposed along the leadbody generally in one quadrant of the helical portion, as defined byillustrative planes 60. Illustrative planes 60 meet at line 70, whichdefines the axis of the bias 50. At least some portion of each electrodeof this embodiment is in this quadrant. By distributing the electrodesin this fashion, the area to be stimulated or sensed by the electrodesupon implantation can have the maximum number of electrodes orientednearby.

For example, if the lead of FIG. 4 were implanted in a rightbrachiocephalic vein with the desired effect of stimulating the rightphrenic nerve or sensing nerve traffic, the quadrant of the bias 50defined by planes 60 could be oriented along the right lateral side ofthe brachiocephalic vein to maximize the effectiveness of anystimulation or signal sensing provided by the electrodes 40.

FIG. 5 is a plan view of a lead in accordance with embodiments of theinvention. This embodiment has a lead body 10 having a proximal portionand a distal end. A bias 50 of a circular or helical basis is proximatethe distal end 30. Electrodes are 40 distributed such that at least aportion of each electrode is within a quadrant of the helix 50 asdefined by illustrative planes 60. This view is of a lead as in FIG. 4,and is taken along line 70.

Implanting a lead in accordance with embodiments of the inventioninvolves advancing the lead to the desired location with the aid of somesort of stiffening or straightening device, such as an internal wire orstylet or external guide catheter. The lead is advanced to the desiredlocation and the stiffening device is removed, allowing the bias torevert to its imparted or natural shape. The lead position is evaluatedthrough X-ray and standard venography techniques. The lead can beadvanced or retracted as necessary, with or without the stiffeningdevice in place. The lead can also be rotated as necessary, again, withor without the stiffening member. In fact, without the stiffening memberin place, the lead can be rotated to reposition the electrodes or insome instances to “tighten” or “loosen” or “expand” the bias 50. Incases where the electrodes on the lead are arranged so that least aportion of each electrode is located within a quadrant of the bias, thelead is oriented so that the tissue of interest to be sensed orstimulated falls within an extension of that quadrant. That is, if oneextends the planes 60 of FIGS. 4 and 5 radially away from line 70 whilethe lead is implanted, the tissue of interest would fall within thequadrant, and preferably toward the center of the quadrant.

FIG. 6 is a schematic view of a lead in accordance with embodiments ofthe invention implanted in a patient. The lead has a lead body 10 havinga proximal portion 20 and a distal end 30. Electrodes 40 are disposed onthe lead body, which includes a bias portion 50. The lead is disposed inthe right brachiocephalic vein 80 of the patient through the subclavianvein 130 and extends into the superior vena cava 90. The transition fromthe right brachiocephalic to the superior vena cava is imprecise, andreferences to the right brachiocephalic vein within this disclosurerefer to both the right brachiocephalic and superior vena cava unlessotherwise indicated. The electrodes 40 are configured to stimulate, orto sense nerve activity of, the right phrenic nerve 100 of the patient.In this embodiment the bias 50 could be a consistent coil diameter, aconverging coil diameter, or a diverging coil diameter.

Veins within the thorax are subject to intrathoracic pressures caused bydiaphragmatic contraction. When the diaphragm contracts, it createsnegative intrathoracic pressures that cause veins within the thorax todilate, increasing venous volume and enlarging the cross sectional areaof the vein. In addition there is a downward translation of the heart110 and lungs that can stretch and elongate the superior vena cava 90and brachiocephalic 80, 120 veins. Pulsing from the cardiac cycle alsocan be translated to the superior vena cava 90 and brachiocephalic 80,120 veins. These physiologic dynamics create many challenges, whichinventors have overcome in leads in accordance with embodiments of theinvention.

The shape of the bias 50 of some embodiments is circular, in the helicalform or in the true circular form. The circular and helical shapes exertforce against the inner luminal surface of the vein creating africtional force that retains the lead in the vein. This radial fixationforce is created by forming a shape or bias in the lead that is“slightly” larger diameter than the vessel diameter. This relationshipcan be described in some embodiments as a bias diameter to vesseldiameter ratio of between 1.1:1 and 1.3:1. The bias 50 diameter in theseembodiments is slightly larger because some of the larger veins in whichthese embodiments are implanted are fairly malleable and the inventorshave found that these veins do not significantly constrain the leads,resulting in bias orientations upon implantation that are substantiallysimilar to the bias' unconstrained position prior to implantation.Inventors have used this knowledge to create desired biases shapes thatare then implanted in much the same configuration.

The bias 50 can be formed in a constant diameter fashion, a diverginghelix or circle, or a converging helix or circle. The different shapesmay be more or less suitable for varying anatomy and differentlocations. If the lead is intended for the junction of the subclavianvein 130 and brachiocephalic vein 80, a converging helix may providesuperior fixation and electrode contact. If the targeted site involvesthe brachiocephalic vein junction or superior vena cava the diverginghelix may be superior. In each case the varying diameters of the coilsmay be proved more intimate contact with the vessel wall for betterfixation and electrode contact. The most proximal portions of the helix(the first ½ to full revolution) may serve as a mechanism of decoupling.This feature may decouple external forces (i.e. arm, shoulder, etc.motion) from the electrodes. It may also permit the bias 50 of the lead,that part that engages the vein, to move (this motion comes fromrespiration, coughing, sneezing, cardiac impulse) independent from theproximal lead portion 20.

In some embodiments, the electrodes 40 are arranged within a quadrant ofthe bias 50 so that they are more apt to stimulate or sense the tissueof interest. In the case where the right phrenic nerve 100 is ofinterest, the lead may be situated so that the most proximal electrodeis located in the subclavian vein and the quadrant of the bias 50 thatincludes the electrodes 40 is places on the right lateral portion of theright brachiocephalic 80. In cases where the electrodes on the lead areoriented so at least a portion of each electrode is within a definedquadrant, the lead could be further oriented so that the quadrant, whenextended, includes a significant portion of the right phrenic nerve.

FIG. 7 is a schematic view of a lead in accordance with embodiments ofthe invention implanted in a patient. The lead has a lead body 10 havinga proximal portion 20 and a distal end 30. Electrodes 40 are disposed onthe lead body, which includes a bias portion 50. The lead is disposed inthe left brachiocephalic vein 150 of the patient. The electrodes 40 areconfigured to stimulate, or to sense nerve activity of, the left phrenicnerve 140 of the patient. In this embodiment the bias 50 could be or aconsistent coil diameter, a converging coil diameter, or a divergingcoil diameter.

The left phrenic nerve 140 passes behind or anterior to the leftbrachiocephalic vein 150 at a somewhat skew angle to the vein 150. Insome embodiments the electrodes 40 may be arranged in the bias 50 sothat they are in the anterior quadrant of the bias 50 as the lead isimplanted. In some of these and other embodiments, the pitch of the coilof the bias 50 may be relatively more circular than helical toconcentrate the electrodes more closely to where the nerve 140 passesclosest to the vein 150. As discussed above, in some embodiments thebias is implanted in the lead and adopts a configuration substantiallysimilar to that of the unstressed unimplanted lead.

FIG. 8 is a schematic drawing of a lead in accordance with embodimentsof the invention implanted in a cross section of a lumen. The lead has alead body 10 and electrodes 40 disposed thereon. The lead body 10 has apreformed bias 50 that forces at least portions of the lead body 10against the walls 160 of a lumen. The lumen has a main axis B that iscoaxial with the bias axis, also B. The lead body has a main axis A, inthis case measured at an exemplary electrode. The angle C between thecoil axis B and lead axis A can be generally described as skew. If thelead body 10 has an axis A more parallel to the coil axis B, the leadbody 10 tends to define an elongated helix that is potentially moresusceptible to motion artifact. Inventors have learned that lead bodieswith their axes A perpendicular to the coil axis B define a helix withgreater stability within a lumen, possibly due to a greater forceapplied transverse to the lumen wall 160.

The fact that the angle C is skew to a significant degree means that thelead body is traversing laterally across the lumen more so thancoaxially. This means that in order for the lead 10 and electrodes 40 tobe close to the lumen wall 160 for stimulation or sensing, the lead 10and electrode 40 combination must approximate the curvature of the lumenwall.

FIG. 9 is a schematic drawing of a lead in accordance with embodimentsof the invention as in FIG. 8 from a view along an axis such as B. Thelead has a lead body 10 form in a circular or helical bias 50, of whichone coil is shown, and an electrode 40. The coil has a diameter D andthe electrode has a length L. In some embodiments, electrodes areappropriately sized in length L relative to coil diameter D. In somecases if the electrode is too long, a circular discontinuity that canseparate, or push away, or prevent intimate contact of the electrodewith the vessel wall is created, leading to a gap 170.

Inventors have found that for some embodiments the ratio of the length Lof the electrode to the diameter D of the coils of the bias 50 can berelevant. For coils configured for implantation into vessels the size ofthe right or left brachiocephalic veins, for example, an effective D:Lratio may be 4:1 or greater. This ratio is particularly relevant whenthe main lead axis A is particularly skew to the lumen axis B asdiscussed with respect to FIG. 8. A sufficient L:D ratio may result inthe lead body adopting a more continuous circular shape that restsagainst the luminal surface 160. It is conceivable that a morecontinuous circular shape will induce less stress, lower opportunity forlumen damage, and thus lower probability of negative tissue response atthe electrode site than a shape with periodic flat areas/sections withcorners. This ratio has application to both the in situ helical andcircular shapes.

One skilled in the art will appreciate that the invention can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the invention is limited only by the claims that follow.

What is claimed is:
 1. A medical electrical lead comprising: a. a leadbody having a preformed helical bias with a coil diameter; b. at leastone electrode; c. wherein the ratio of the coil diameter to the lengthof the at least one electrode is at least 4:1.
 2. The medical electricallead of claim 1, wherein the ratio of the coil diameter to the length ofthe electrode is at least 5:1.
 3. The medical electrical lead of claim1, wherein the ratio of the coil diameter to the length of the electrodeis at least 6:1.
 4. The medical electrical lead of claim 1, wherein thepreformed helical bias is a converging helical bias and the coildiameter is defined as the diameter of the smallest coil of the bias. 5.The medical electrical lead of claim 4, wherein the ratio of the coildiameter to the length of the electrode is at least 5:1.
 6. The medicalelectrical lead of claim 4, wherein the ratio of the coil diameter tothe length of the electrode is at least 6:1.
 7. The medical electricallead of claim 1, wherein the preformed helical bias is a diverginghelical bias and the coil diameter is defined as the diameter of thesmallest coil of the bias.
 8. The medical electrical lead of claim 7,wherein the ratio of the coil diameter to the length of the electrode isat least 5:1.
 9. A medical electrical lead comprising: a. a lead bodyhaving preformed helical bias with a coil diameter; b. a plurality ofelectrodes; c. wherein at least a portion of each of the plurality ofelectrodes is within a single quadrant of the helical bias.
 10. Themedical electrical lead of claim 9, wherein each of the electrodes has alength such that ratio of the coil diameter to the lengths of theelectrodes is at least 4:1.
 11. The medical electrical lead of claim 9,wherein each of the electrodes has a length such that ratio of the coildiameter to the lengths of the electrodes is at least 5:1.
 12. Themedical electrical lead of claim 9, wherein each of the electrodes has alength such that ratio of the coil diameter to the lengths of theelectrodes is at least 6:1.
 13. A medical electrical lead comprising: a.a lead body having a lead body axis; b. a preformed bias in the leadbody, the bias having a bias axis; c. wherein the angle between the leadbody axis and the bias axis is greater than thirty degrees.
 14. Themedical electrical lead of claim 14, wherein the angle between the leadbody axis and the bias axis is greater than forty-five degrees.
 15. Amethod of implanting a lead in a lumen, the method comprising: a.inserting a lead in a lumen, the lead having a helical bias and aplurality of electrodes wherein at least a portion of each of theplurality of electrodes is within a single quadrant of the helical biasb. positioning the lead within the lumen so that a tissue of interest iswithin the quadrant as the quadrant extends outward radially.
 16. Themethod of claim 15, wherein the lumen comprises the rightbrachiocephalic vein and the tissue of interest comprises the rightphrenic nerve.
 17. The method of claim 15, wherein the lumen comprisesthe left brachiocephalic vein and the tissue of interest comprises theleft phrenic nerve.
 18. The method of claim 15, wherein the lumencomprises the superior vena cava and the tissue of interest comprisesthe right phrenic nerve.
 19. The method of claim 15, wherein the lumencomprises the right internal jugular vein and the tissue of interestcomprises the hypoglossal nerve.
 20. The method of claim 15, wherein thelumen comprises the junction between the right brachiocephalic vein andthe right subclavian vein.